Storage tank for storing two fluids



United States Patent Primary Examiner-George E. Lowrance Attorney -Thedore E. Bieber and .l. H. McCarthy ABSTRACT: A fluid storage tank for storing two fluids of variable volumes, for example, oil and gasoline in which a rigid outer shell forms a first fluid storage chamber and an enclosed flexible wall located within the outer shell forms a second fluid storage chamber, the flexible wall permitting variable volumes to be stored in the two chambers. The outer shell is formed with an inlet and outlet to the first storage chamber and access is gained to the second fluid storage chamber by means ofa flexible conduit extending through the first fluid storage chamber in communication with the space outside the storage tank and the first fluid storage chamber.

[72] inventors Robert G. Fallows Cheshire; Joseph E. Conder, Denbighshire, England [21] Appl. No. 807,384 [22] Filed March 14, 1969 [45] Patented Nov. 3,1970 [73] Assignee Shell Oil Company New York, New York a corporation of Delaware [32] Priority March 20, 1968 [33] Great Britain [3 l 13,461/68 [54] STORAGE TANK FOR STORING TWO FLUIDS Claims, 4 Drawing Figs.

[52] US. Cl .J 220/22,

270/85 [51] Int. Cl 865d /06, 865d 25/18 Field ofSearch 220/20, 22, 85, A, 85B

Patented Nov. 3, 1970 3,537,608

' INVIENTORSI ROBERT e. FALLOWS JOSEPH E. CONDER 1 STORAGE TANK FOR sromno 'IWO FLUIDS BACKGROUND OF THE INVENTION to meet the above demandsand a considerable saving could be achieved if the same storage tanks could store both gasoline and gas-oil without risk of cross-contamination and without the need ofexpensive tank cleaning operations.

SUMMARY OF THE INVENTION According to the present invention, a flexible curtain or membrane for dividing the interior of a storage tank into two separate compartments of variable volume comprises a cellulose layer coated on both sides with atleast one layer of a polyurethane. The cellulose layer is preferably ethyl cellulose/cellulose acetate; In order to increase the mechanical strength of the curtain required for use in large storage tanks it is preferably to form the curtain from a plurality of polyurethane coated cellulose layers laminated together.

Preferably the curtain is formed from a plurality of individual panels, each panel comprising a plurality of polyurethane coated cellulose layers which are laterally offset or staggered with respect to one another, whereby the resulting stepped longitudinal edges of adjacent panels mate and are bonded together to complete the curtain.

A storage tank embodying a curtain according to the invention comprises a rigid outer enclosed shell and a compartment of variable volume disposed within the shell, the compartment having a displaceable rigid roof structure attached to the upper end of the curtain, the lower end of the curtain being secured to a peripheral skirting ring within the shell.

Preferably the rigid roof structure is conicaland contains a buoyant material to enable'theroof to float upon the product to be stored within the compartment.

DESCRIPTION OF THE DRAWINGS The invention will be described further, by way ofexample, with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic sectional elevation of a storage tank having inner and outer storage compartments;

FIG. 2 is a view similar to FIG. 1 showing the inner compartment in a fully collapsed condition;

FIG. 3 is a sectional detail, to an enlarged scale, of the construction ofthe inner compartment, and FIG. 4 is an enlarged detailed view ofa section ofa curtain.

DESCRIPTION OF'THE PREFERRED EMBODIMENT A tank for the storage of gasoline and gas-oil comprises an outer rigid shell 1 housing a compartment 2 of variable volume. The outer shell] has a base 3, side wall or walls 4 and a roof 5. The compartmentZ bounded by a rigid conical roof 6 and a flexiblecurtain 7. The top of the curtain is attached to the periphery of the roof 6 whilst the bottom of the curtain is attached to a skirtingringS running around the base of the interior ofthe shell 1.

The conical roof6 is internally lined with a buoyant material 9, such as a polyurethane foam, in order that the roof will at all times float at a substantially level condition on gasoline to be stored within the compartment 2; The interior of compartment 2 is vented to atmosphere through a flexible pipe 10 coupling an outlet port 11 at the centre ofthe conical roof6 to a port 12 in the roof 5 of the rigidshell I. The interior of the rigid shell is vented to atmosphere through a port 13in the roof of the shell. Inlet ports 14 and 15 communicate respectively with the interiors of the rigid shell and the variable compartment 2. Gas-oil is introduced into the shell 1 through port 14 and gasoline is introduced into compartment 2 through port 15. The base 3 of the rigid shell carries roof supports 16 which support the conical roofwhen the inner compartment is in a fully collapsed condition as depicted in FIG. 2. The roof supports 16 prevent the roof6 from approaching too close to the skirting ring 8. Should this happen the curtain 7 is liable to be trapped and damaged between the roof 6 and the ring 8. The curtain is attached to the periphery of the roof 6 and to the skirting ring 8 by means of studs and clamping rings 17 shown in FIG. 3. The studs pass through apertures spaced along the top and bottom edges ofthe curtain.

The curtain must be substantially impervious to the products to be stored within the tank in order to prevent contamination of one product with the other and must be of sufficient mechanical strength to withstand folding and scuffing as the roof6 moves up or down within the shell due to changes in volume of the gasoline stored within the inner compartment 2.

The curtain is formed by coating a cellulose layer, preferably an ethyl cellulose/cellulose acetate layer with polyurethane. The coating can be carried out by spraying,

brush coating, calendering or dipping techniques. The cellulose layer is substantially impervious to gasoline but by itself has little strength and scuff-resistance. Polyurethane, however, has good strength and scuff-resistance properties and serves to protect the cellulose layer from physical damage. In the spraying technique, the polyurethane mix is prepared with a solvent in order to reduce its viscosity. Each side of the cellulose layer is sprayed with at least two layers of polyurethane. The cellulose layer employed is preferably that known as Sidac 600 PT and when coated on each side with two layers of polyurethane the overall thickness of the laminate so formed is 0.015 of an inch. Brush coating and dip coating produce a faster'buildup of polyurethane than the spraying technique.

If necessary, a reinforcement fabric can be applied to the curtain at particular points, such as the points of attachment of the curtain to the roof and skirting ring. A suitable reinforcement material can be produced by dip coating in polyurethane an open weave cloth.

Whilst a curtain can be formed from a single cellulose layer coated on both sides with polyurethane it is preferably to form the curtain from a number of such coated layers. Thus, a curtain can be formed from a lamination ofthree coated cellulose layers bonded together with polyurethane. Furthermore, for large storage tanks, it is impractical to manufacture the curtain in one piece. Consequently, the completed curtain is made up from a number of panels 19. The polyurethane coated cellulose layers of each panel 19 are laterally offset or staggered as shown in FIG. 4 to produce stepped longitudinal edges. The top and bottom of each panel are perforated as shown at 18 to receive the fixing studs 17. When the panels are suspended from the conical roof the stepped longitudinal edges of adjacent panels mate one with the other and are welded together with polyurethane to form a sealed joint thus completing the curtain.

In practice, gasoline is stored within the inner compartment 2 and gas-oil within the rigid shell outside the inner compart ment. The roof floats on the gasoline at a substantially even level by virtue of the buoyancy provided by the polyurethane foam 9'at the apex of the cone. As the roof6 is of conical configuration gas-oil readily drains off and, furthermore, air which is trapped within the inner compartment during the filling thereof with gasoline collects at the apex of the conical roof and is vented to atmosphere through the flexible pipe 10.

As the curtain is substantially impermeable to the gas-oil and gasoline to be stored within the two compartments within the shell it is possible for the one tank to store both products without risk of any substantial degree ofcross-contamination. It is, therefore, no longer necessary to clean out a tank prior to the introduction of a different product. It is envisaged that during winter months, the inner compartment will be in its fully extended position filled with gasoline. On the other hand,

during the summer months when there is an increased demand for gasoline, the inner compartment will be in its collapsed condition and the storage tank will be substantially full of gasoil contained therein to meet the heavier demands on this fuel during winter months.

We claim: 1. A fluid storage tank for storing two fluids of variable volumes, said tank comprising:

an enclosed outer shell having a base member, side wall and a top closure defining a first fluid storage chamber; an enclosed flexible wall concentrically arranged within said outer shell and having the lower edge thereof attached to said base member thereby defining a second fluid storage chamber; roof means attached to the upper edge of said flexible wall means to thereby enclose said second fluid storage chamber;

' first fluid storage chamber inlet means extending through said outer shell near the upper end thereofin communication with the space outside the storage tank and said first fluid storage chamber;

first fluid storage outlet means extending throughsaid shell near the lower end thereof;

flexible conduit means extending through said first fluid storage chamber in communication between the space outside the storage tank and said second fluid storage chamber to thereby provide a second fluid storage chamber inlet; and

second fluid storage outlet means extending through said base member of said outer shell and in communication between the space outside said storage tank and said second fluid storage chamber, whereby said second fluid storage chamber is free to expand or contract by virtue of said flexible wall member to thereby accommodate varying volumes of fluid in said first and second fluid storage chamber.

and spaced therefrom to thereby limit the lowermost position of said roof means.

5. A fluid storage tank as defined in claim 4 wherein said roof support means comprise a plurality of upstanding pedestals attached to said base member.

6. A fluid storage tank as defined in claim 1 wherein said wall of said shell and said flexible member as substantially cylindrical.

7. A fluid storage chamber as defined in claim 6 wherein said top closure of said shell in said roof means are substantially conical.

8. A fluid storage tank as defined in claim 1 wherein said flexible wall member comprises a layer of cellulose coated on both sides with at least one coating of polyurethane on each side ofsaid cellulose layer.

9. A fluid storage tank as defined in claim 1 comprises a plurality of polyurethane coated cellulose layers laminated together.

10. A fluid storage tank as described in claim 1 wherein said flexible wall comprises a plurality of individual panels, the polyurethane coated layers of each panel being offset with respect to one another to thereby form step longitudinal panel edges, the step edges of adjacent panels being bonded together to form said flexible wall member. 

